The coupling mechanism between a cell membrane receptor and changes in this membrane properties which lead to the eventual response is a central problem in biology. In several cell types a change in the plasma membrane permeability to cations, notably Ca+2 ions has been shown to occur upon ligand activation of specific membrane receptors. Mast cells and basophils carry high-affinity FcEpsilon receptors on their membranes which, upon crosslinking cause degranulation and mediators secretion. One prominent step in the sequence of events linking FcEpsilon aggregation to secretion in the influx of Ca+2 ions. Two membrane protein components constituting its ligand-operated Ca+2 channel, responsible for coupling the immunological stimulus, have been isolated in high purity from the rat basophilic leukemia line 2H3. This project proposes to characterize the Ca+2 channel forming protein (cromolyn binding protein - CBP) of these cells and its interactions with the FcEpsilon receptor. It will encompass biochemical, immunochemical and electrophysiological studies aimed at the characterization of the receptor operated calcium channel activity of the RBL 2H3 cells. This will be done on vesicular or planar model membranes reconstituted with the pure proteins. The relevance of results obtained in the latter systems to the function of the intact cell will be pursued. Problems to be addressed are the chemical nature and structural properties of the CBP; identification of the subunit(s) interacting with the CBP; stoichiometry of the different components required for channel activity and physico-chemical characterization of the ion channel. Apart from their fundamental significance, IgE-receptor aggregation and ion channel activation are the key initial events in mast cell and basophil degranulation, which, in turn are assumed to be the main pathological mechanism of the immediate type allergic reactions. Hence this project may potentially provide new ideas and means for novel therapeutic approaches to this widespread health disorder.